This invention relates to cartons with hinged covers which are formed from sheets of plastic materials by a thermoforming process. The invention is particularly applicable to egg cartons but may be applied to other types of cartons also, especially those which are used to carry fragile articles in separate packaging cells within the carton.
Egg cartons used in the retail marketing of eggs have, up to the present, usually contained one dozen eggs packaged in two rows of six eggs each. These cartons, which may be made of wood pulp or, more recently, of thermoformed plastic, generally comprise a bottom section containing the egg-receiving cells, a cover which is generally in the form of an inverted dish-like lid and a locking flap which engages with the cover to hold it closed. Various locking devices have previously been described or used. U.S. Pat. Nos. 3,337,110 and 3,356,284, for example, describe cartons which have a locking flap on the bottom section with a locking detent which engages with a locking flange on the cover. U.S. Pat. No. 3,648,916 describes a carton with a latching flap on the bottom section which has wedge-shaped recesses matching similar recesses on the cover. Latching bars on the recesses engage detents on the cover to provide the desired locking. Similar locking devices are shown in U.S. Pat. Nos. 3,687,350; 3,735,917; 3,817,441 and 3,908,891.
In some markets, eggs are sold in cartons of eighteen eggs, rather than in the traditional carton of one dozen. In the past, eighteen cell egg cartons have been thermoformed from plastic sheet only in versions which do not have complete protective covers although an eighteen cell carton with a protective cover has been produced in molded pulp. It would be desirable to be able to make an eighteen cell egg carton with an integral protective cover but the existing covered eighteen cell cartons such as the pulp carton presently on the market, cannot be thermoformed from plastic sheet. One reason is that the latch on the pulp carton has long elements, which, if thermoformed, would require a small, relatively narrow piece of the plastic sheet to be drawn a long way beyond the sheet line. In thermoforming, long extensions beyond the sheet line are generally undesirable because they produce considerable weakening.
On the other hand, it is not practicable to enlarge thermoformed plastic cartons of existing types by the inclusion of a third row of six egg cells, to form an eighteen cell carton because the enlarged cartons could not be accommodated on existing packaging equipment, a large amount of which is in use. Conventional packaging equipment is capable of accepting either covered twelve cell cartons with conventional locking flaps or the eighteen cell covered pulp cartons, both of which are small enough to fit within the equipment. If the twelve cell thermoformed plastic cartons were enlarged to hold eighteen eggs, the carton in the open position would exceed the maximum acceptable dimensions of 30.times.30 cm. (12.times.12 inches). The covered pulp carton mentioned above can be used on conventional equipment because its locking elements extend upwards from the lower section of the carton rather than sideways, as the locking flap does on the conventional plastic cartons.
The parent applications identified above describe a carton which is capable of holding eighteen eggs while still being filled on conventional packaging equipment. That carton has been successfully used in the packaging and marketing of eggs in eighteen cell lots.
It is desirable to increase the size of the egg cells in such a carton so that they can accommodate jumbo sized eggs. Moreover, it is desirable to increase the size of the cells without increasing the overall plan dimensions of the carton so that it can be filled on existing equipment.
It is an object of the present invention to provide a carton with enlarged cells which has a positive locking latch and which can be filled on existing machinery.